(a) Technical Field
The present disclosure relates to a vehicle seat and a method for controlling a sitting position using the same, more particularly, to the vehicle seat capable of implementing a neutral position for reducing fatigue at the time of driving.
(b) Description of Related Art
In general, a seat installed within a vehicle essentially includes a seat cushion 100 that touches the driver's or passenger's hips and a seat back 200 that touches the driver's or passenger's back, as illustrated in FIGS. 14 and 16. In addition to the essential components of the seat, the seat includes a seat lifter for adjusting the height of the seat cushion 100, e.g., as disclosed in Korean Patent Application Publication No. 10-2018-0005344, a tilting device to adjust the angle of the seat cushion 100, a seat adjustment device such as a recliner 300 to adjust the angle between the seat cushion 100 and the seat back 200, e.g., as disclosed in Korean Patent No. 10-1526979.
Meanwhile, in order for a driver to drive a vehicle, the driver sits down and grasps a steering wheel with both hands. If the driver drives the vehicle for a long time, a load is concentrated in the vicinity of the driver's lumbar vertebra and hips, causing blood pooling thereon. Accordingly, the driver may feel extreme fatigue in accompaniment with leg numbness and swelling and the like. A number of these symptoms occur especially in a human thigh with the slowest flow of blood. Further, it may cause back pain, a slipped disk, etc. due to the concentration of load on a specific portion when driving for a long time. Thus, there is an increasing need for a seat capable of implementing an optimal driving position to reduce fatigue by distributing the load concentrated on the specific portion of the human body at the time of driving and by lessening strain on joints and relaxing muscles even while driving for a long time.
Meanwhile, the neutral position illustrated in FIG. 13 is known as a type of position for reducing fatigue. The neutral position is the most comfortable position for the human body in a weightless environment, and it is known as a position for lessening strain on joints and balancing the human body by optimizing an angle between a calf and a thigh, an angle of the thigh to the ground, an upper/lower body angle between an upper body and a lower body, and an upper body's horizontal angle to the ground.
To implement a reduction in fatigue in the neutral position, a horizontal angle of the human thigh to the ground is especially important. The thigh's horizontal angle is a criterion when setting the upper/lower body angle and the upper body's horizontal angle because the slowest flow of human blood occurs in the thigh as described above. Accordingly, for the implementation of the neutral position, it is necessary to set the thigh's horizontal angle to be equal to or higher than at least 28° such that blood is able to smoothly flow in the thigh by increasing a difference in elevation.
However, when the seat height is adjusted to secure a driver's forward field of view according to the body type thereof in the conventional seat, both front and rear ends of the seat cushion 100 are simultaneously moved up or down, as illustrated in Korean Patent Application Publication No. 10-2018-0005344 and FIG. 14.
An apparatus for adjusting the height of a vehicle seat is illustrated in FIG. 15. The height of the vehicle seat illustrated in FIG. 15 is adjusted by pivoting a four-bar link that includes a seat cushion frame 2a, front and rear links 6a and 13a pivotably connected to respective front and rear ends of the seat cushion frame 2a, and a fixed part 7a for pivotably supporting the front and rear links 6a and 13a through a fixed part bracket 9a. 
As illustrated in FIG. 15, when the four-bar link is pivoted, both of the seat cushion frame-side end of the front link 6a and the seat cushion frame-side end of the rear link 13a are simultaneously pivoted in the same direction (upward). Thus, both of the front and rear ends of the seat cushion 100 are lifted up. In this state, when the four-bar link is pivoted in the opposite direction again, both of the seat cushion frame-side end of the front link 6a and the seat cushion frame-side end of the rear link 13a are simultaneously pivoted in the same direction (downward). Thus, both of the front and rear ends of the seat cushion 100 are moved down.
Hence, it is impossible for the conventional seat height adjustment apparatus to implement the thigh's horizontal angle in the neutral position.
Meanwhile, when a tilting operation is performed to adjust the angle of the seat cushion 100 for increasing the support of the thigh during rapid braking of the vehicle, only the front end of the seat cushion 100 is lifted up or down, as illustrated in Korean Patent No. 10-1526979 and FIG. 16.
An apparatus for adjusting the height of this vehicle seat is illustrated in FIGS. 17A and 17B. The angle of the vehicle seat illustrated in FIG. 17A is adjusted by pivoting a five-bar link that includes a seat cushion frame 2b, a first front link 6b and a rear link 13b pivotably connected to respective front and rear ends of the seat cushion frame 2b, a second front link 35b, the other end of which is pivotably connected to a fixed part 7b, and the fixed part 7b for pivotably connecting the rear link 6b to the second front link 35b. 
As illustrated in FIG. 17B, when the five-bar link is pivoted in the counterclockwise direction about the center of rotation of the rear link 13b, only the front end of the seat cushion frame 2b is lifted up. Thus, the height of the seat cushion 100 is generally moved up, with the consequence that the hip point of the driver is also moved up.
If the hip point is moved up when the seat cushion 100 is tilted, the variation of the thigh's horizontal angle is small compared to the level that the knee portion is moved up. Accordingly, if the tilting angle is forcedly increased to implement the neutral position, the driver's position is generally moved up, which may lead to a reduction in headroom and a knee space, as illustrated in FIG. 18A. Hence, it is impossible to substantially implement the neutral position illustrated in FIG. 13 because the seat cushion 100 is very restrictively tilted in a passenger vehicle such as a sedan having very limited headroom and knee space.